System and Method for Aircraft Cabin Atmospheric Composition Control

ABSTRACT

Method and arrangement for adjusting nitrogen and oxygen concentrations within regions of an aircraft. The method includes separating nitrogen from ambient air onboard an aircraft thereby establishing a high-concentration nitrogen supply and then dispensing high-concentration nitrogen from the supply to a fire-susceptible, non-habitable region of the aircraft where the high-concentration nitrogen is reservoired thereby decreasing the capability for the atmosphere therein to support combustion. Oxygen is also separated from the ambient air thereby establishing a high-concentration oxygen supply that is dispensed to an occupant cabin of the aircraft thereby increasing the level of oxygen concentration within the cabin to a level greater than the naturally occurring concentration of oxygen at the experienced internal cabin pressure. When it is determined that reduced oxygen concentration is required in the occupant cabin, the reservoired high-concentration nitrogen is moved into the passenger cabin diluting the oxygen-elevated environment.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 10/708,217 which was filed on Feb. 17, 2004 and claims thebenefit of U.S. Provisional Application No. 60/447,627 filed on Feb. 15,2003, pursuant to 37 CFR 1.53(c).

BACKGROUND OF INVENTION

1. Technical Field

The present invention relates to systems and methods for selectivecontrol of the balance between nitrogen and oxygen content in the air inhabitable and non-habitable areas of pressurized spaces within aircraft.More particularly, the invention relates to systems to alter the balancebetween oxygen and nitrogen in different areas of aircraft to createzones where the atmospheric composition more properly supports the needsof the zones. The invention accomplishes this zonal compositionoptimization by directing a higher percentage of the oxygen available inthe air entering the aircraft into the habitable areas, while directinga higher percentage of the available nitrogen in the air into thenon-habitable areas, especially those areas of greater flammability riskand/or limited access in case of fire.

2. Background Information

The reduced air pressure available in pressurized aircraft cabinsresults in molecular concentrations of oxygen that are far lower thanthose for which most passengers are physiologically adapted. This causesreduced levels of blood and tissue oxygenation (see FIGS. 1 and 2) andthe initiation of physiological changes related to the body's efforts tocompensate and adapt. The resulting physiological stresses includereduced respiratory effectiveness, compensatory increases in heart andrespiration rates, increased levels of blood clotting factors, andincreased production of red blood cells. These physiological changesresult in, or contribute to, a variety of negative impacts, includingbut not limited to fatigue, reduced mental and physical performance,drowsiness, impaired visual acuity, impaired sleep, and possibly theformation of blood clots. In fact, it is well accepted that visualacuity has begun to fall off as early as 7500 feet, yet commercialairlines are legally permitted to maintain pressures equivalent to 8000feet within the aircraft. As such, a certain compromise in the flightcrew's capabilities have been determined acceptable, though notdesirable. The present invention provides methods and systems forreducing, if not obviating, these and other detrimental affects sufferedby passengers and flight crew on civilian aircraft.

Standard atmospheric pressure at sea level is 14.7 psia. Thecorresponding oxygen pressure (partial-pressure) at sea level isapproximately 3.07 psia. When atmospheric pressure is reduced, airexpands and the molecular concentration of oxygen and the other gasesthat make up air are proportionately reduced according to Dalton's Law.

Pressurized aircraft cabins provide air pressures ranging fromapproximately 10.91 psia (8000 ft equivalent cabin altitude) to 11.78psia (6000 ft equivalent cabin altitude) when the aircraft are operatingat their maximum cruise altitudes. These reduced cabin pressures resultin oxygen partial pressures ranging (approximately) from 2.286 to 2.468psia.

Aircraft pressurization systems maintain cabin pressure levels thatallow passenger and crew habitation while the aircraft flies ataltitudes far above those at which human beings could otherwise survive.Current pressurization systems maintain cabin air pressures between74-80% of the standard sea level atmospheric pressure.

As a prophylactic against unexpected low-pressure experiences, andconsequently low-oxygen conditions which could adversely affectperformance, cockpit crew members are provided with pressure demandoxygen masks for use when the aircraft is unable to maintain adequatepressurization. The sources of direct oxygen may also be used in casesmoke fills the cockpit, or under certain other scenarios as required bycivil aviation regulations.

Emergency oxygen is provided in the passenger cabin in the form of dropdown masks that activate automatically when air pressure in the cabinfalls to levels at which passenger safety is at imminent risk.Therapeutic oxygen outlets are sometimes provided for use by passengerswho require continuous supplemental oxygen due to medical conditions.Aircraft are also often equipped with portable “walk-around” oxygenbottles for the crew to use during brief periods when their dutiesrequire them to leave their seats while the aircraft is experiencingpressurization problems. A common problem of all of these supplementaloxygen delivery systems, however, is that they require tubes connectedbetween an oxygen source and the delivery mask for the user. Such tubes,like other cords in the occupied compartments of an aircraft, have beenrecognized as hazards, particularly in emergency situations. It can beimagined that in an emergency situation where the environment is alreadychaotic, the deployment of potentially entangling oxygen delivery tubesand masks, including their elastic securement straps, detrimentallyimpacts the cabin environment.

As indicated above, conventional wisdom in aircraft design has focusedon pressurization with regard to increasing the habitability of aircraftcabins. Traditionally, aircraft are pressured toward a sea-levelequivalent; but in actuality, altitude equivalents on the order of 6000to 8000 feet are actually achieved. Resultantly, a correspondingdecrease in oxygen concentration has been accepted. Because thesecorresponding oxygen concentrations are generally suitable formaintaining perceivable occupant comfort, little attention has beendirected toward consequential affects suffered by cabin occupants.

“Perceived comfort” is addressed because most passengers are unawarethat certain physiological changes take place responsive to reducedoxygen concentration experienced onboard aircraft, including increasedrespiratory and heart rates. It is for this reason that many persons areadvised not to fly. For instance, persons who have recently undergonesurgery which makes them particularly vulnerable to these physiologicalchanges may be advised not to fly. Still further, persons havingpredispositions to such ailments as heart attacks and strokes are oftenadvised not to fly by their medical caretakers. Elderly persons, andothers with unappreciated risk factors for such ailments do fly, butresultantly place themselves at undue risk of suffering a debilitating,or life-threatening incident. It is known that the decreasedconcentration of oxygen in aircraft have the potential for contributingto these incidents, but as discussed above, aircraft pressurizationlimitations have been heretofore viewed as a limiting constraint againsttheir remedy.

The focus on pressure is due, at least in part, to the fact thatairframes are not designed to accept greater levels of pressurization,which in turn produce greater differential pressures across the fuselageskin. In fact, this limitation associated with the airframe'scapabilities to endure greater pressure differentials thereacross hastraditionally imposed reduced oxygen levels on passengers because of theheretofore accepted limitation on pressurization. Still further,aircraft operators are resistant to increasing interior pressurizationbecause it significantly increases operating costs and limits aircraftperformance.

Deep Vein Thrombosis (DVT), a syndrome or condition which has recentlygarnered increased attention with respect to airline travel, posessignificant risk to cabin occupants, as well as those businesses thatare tied in with the industry. Because the incidence of deep veinthrombosis has caught the eye of the public, the press has capitalizedthereupon and dubbed the syndrome as “economy class syndrome.”Heretofore, the focus has been on the confining and cramped nature ofairline seats, particularly in economy class, and the restrictions thatare resultantly imposed upon passenger mobility. Certain studies,however, have indicated that the cramped nature of smaller seats onlycontribute to the inducement of deep van thrombosis rather than causeit. In fact, those same studies tend to indicate that this malady stemsprimarily from other conditions experienced during airline travel.

Those factors which are either known or expected to contribute to theinducement of deep vein thrombosis include mobility restrictions whichcorrespondingly reduce blood flow movements thereby placing a person athigher risk for forming blood clots, dehydration caused by the dryinterior atmosphere of the aircraft and which can be exacerbated by thediuretic-effects of alcohol, and pressure related aspects. An increasedtendency to develop blood clots as a result of conditions on an airlinerare the hallmark of this syndrome. One aspect of great importance, butwhich has attracted less attention, is physiological effects caused byaltitude adaptation. When exposed to reduced pressure and acorresponding reduction in oxygen concentration, the body immediatelyattempts to compensate. This phenomenon is well appreciated at least byathletes who often train at high altitudes to enhance their performanceat lower altitudes. It is known that the body adjusts by making certainphysical changes. Among others, the concentration of red blood cells isincreased thereby improving the capacity for carrying oxygen. Forairline passengers, the effect, however, is detrimental. It has beenobserved that persons who are exposed to the reduced pressure and oxygenlevels that are experienced in-flight have a substantially immediateincrease in certain clotting factors within their blood. This increasehas been measured to vary between three and eight times the levelpresent in persons immediately before flight. Such a high level responseis equivalent to that which the body undergoes as a reaction tosignificant trauma or injury.

A hallmark of the present invention(s) is the previously unappreciatedconnection between the reduction in oxygen concentration experiencedin-flight and the increased blood clotting factors that result and whichultimately impact the incidence of deep vein thrombosis suffered as aresult of airline travel.

The invention also addresses fatigue, comfort and physiological stressissues which result from the practical limitations of aircraftpressurization systems, which existing oxygen delivery and controlsystems are either incapable of addressing or are not suitablyconfigured.

SUMMARY OF INVENTION

In exemplary embodiments, the present invention takes the form of anapparatus and method for controlling the oxygen concentration inaircraft cabins and non-habitable areas by proportionately increasingthe oxygen content of the air going to the cabin while at the same timeproportionately decreasing the oxygen content of air going tonon-habitable areas. The apparatus incorporates redundant oxygen andpressure sensors to monitor the oxygen concentration in the cabin air.Oxygen content is continually monitored and adjusted to achieve andmaintain an atmosphere in the passenger cabin that is sufficientlyoxygen enriched to address the oxygen related impacts of reduced airpressure, while limiting the degree of oxygen enrichment to prevent thecreation of an atmosphere that increases material flammability abovesafe and certifiable levels. At the same time, the apparatus continuallymonitors the oxygen content in non-habitable pressurized areas tomaintain an atmosphere with reduced ability to sustain combustion, andto allow storage of a nitrogen cache for use in re-balancing the cabinoxygen/nitrogen balance to natural levels in case of smoke/firedetection in the cabin.

The invention alters the gas composition of the cabin air to increasethe partial pressure of oxygen. The increased partial pressure of oxygenis achieved without altering the cabin air pressure or the differentialpressure between the interior and exterior of the fuselage, and withoutincreasing the overall content of oxygen inside the pressure vessel ofthe aircraft. The cabin partial pressure of oxygen is monitored andadjusted continuously to provide the desired atmospheric oxygenenrichment while preventing the creation of an atmosphere whichincreases material flammability in the cabin above FAA approved levels.In this regard, it should be pointed out that the concentration ofoxygen will always be less than that encountered naturally at sea level,and therefore an inherently acceptable concentration for safe operation.

In at least one embodiment, the generation of oxygen has as a byproductthereof the generation of flame-inhibiting nitrogen. In another aspectof the present invention(s), this byproduct-nitrogen is supplied toareas and/or compartments of the aircraft particularly susceptible tofire hazards. For instance, the nitrogen can be injected into thecabling ducts, baggage compartment, radio rack compartments, as well asother areas where electrical wiring and other high-fire-risk assembliesare concentrated. The nitrogen may also be reservoired for distributionto burning or smoldering areas should onboard combustion occur. In afurther aspect, the current invention contemplates providing thecapability for rapidly inter-mixing the reservoired nitrogen into theraised oxygen concentration areas in the event that an elevated andundesirable combustion-risk condition is determined, or an actualcombustion situation is detected or otherwise signaled.

As an adjunct to the nitrogen-based fire inhibiting arrangement andmethod, it is further contemplated that smoke and fire sensors can beadvantageously placed in return air ducts of the aircraft therebyenabling earlier detection and extinguishment than current systemsallow.

Further features and advantages of the present invention will bepresented in the following detailed description of a preferredembodiment of the invention.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a graphical representation of oxygen saturation compared tocorresponding pulse rates of a subject take at the indicated timeintervals on a MD11 aircraft flying from London, UK to Atlanta, US;

FIG. 2 is a graphical representation corresponding to FIG. 1, but inwhich temperature, pressure and RH (%) are comparatively demonstrated;

FIG. 3 is a graphical presentation of a subject's pulse rate in responseto varying oxygen saturation levels and compositional percentages at sealevel;

FIG. 4 is a highly simplified schematic representation of an exemplarysystem configured according to one embodiment of the present inventionin which nitrogen and oxygen are separated and reservoired in segregatedareas, but with a rapid re-mixing capability between the reservoirs;

FIG. 5 is a schematic plan view representation of an exemplary systemconfigured according to the present invention and shown positionedwithin an aircraft fuselage;

FIG. 6 is a schematic elevational view representation of a systemcorresponding generally to that illustrated in FIG. 5;

FIG. 7 is a detail schematic view of an exemplary gas separator suitablefor utilization in the present invention;

FIG. 8 is a detail schematic view of an exemplary oxygen distributionduct, including the end portions taking the form of piccolo tubes;

FIG. 9 is a detail schematic view of an exemplary nitrogen distributionduct, including the graduated piccolo tubes; and

FIG. 10 is a O2/N2 control logic/function table demonstrating varioussystem responses to an array of input variables.

DETAILED DESCRIPTION

FIGS. 1 and 2 graphically demonstrate easily monitored physiologicalreactions to airline flight. In the example of FIG. 1, a subject's heartrate 10 (linearized 11) is compared to experienced oxygen saturationlevels 12 (linearized 13). Further details of the experienced cabinenvironment are illustrated in FIG. 2 where temperature 15, pressures 16and relative humidity 17 (linearized 18) are tracked with respect totime for the trip of FIG. 1. The relationship of increasing heart rateto decreasing oxygen saturation levels is readily appreciated. Thissignificant bodily reaction, however, goes substantially unnoticed bythe passenger. A similar reaction is shown at sea level in FIG. 3 whereheart rate 21 clearly tracks oxygen content (percentage basis 20,saturation basis 22) in the air.

Therefore, as described above, in one aspect the present inventionconstitutes raising the atmospheric concentration of oxygen withinaircraft occupant compartments, without increasing pressurization.Several different systems and technology are contemplated as suitablefor increasing cabin oxygen concentration levels. In a most rudimentarysense, bottled oxygen can be utilized, but certain drawbacks areappreciated such as increased weight and onboard space occupation thatsuch systems would require. Functionally, however, such systems would beacceptable. Liquid oxygen also serves as a suitable supply, but forcommercial use is likely impractical and not cost-effective.

The preferred systems for providing oxygen for increasing concentrationlevels within aircraft occupant cabins are those which produce highconcentration oxygen via separation from available atmospheric air.Examples include membrane filter methods, electro-chemical methods,superconducting magnetic screens, and molecular sieves, among others.Particularly preferred is the molecular sieve method in which oxygen isphysically separated from the other constituent components of ambientair.

In an exemplary embodiment of such molecular sieves, zeolite material isformed into a bed through which pressured ambient air is forced. As aresult, oxygen is permitted to pass therethrough, while other componentsof the air, primarily nitrogen (but also carbon dioxide and water), areheld back and absorbed in the zeolite bed via molecular absorption. Aswill be appreciated by those persons skilled in this art, the bed willbecome saturated and have to be purged of the absorbed components. Thismay be accomplished in a number of ways, but that which is most commonis to relieve the imposed pressure and permit the absorbed gases todefuse from the zeolite material.

Because of the low-pressure environment in which aircraft operate,certain airborne molecular sieve air separators depend on the ability topurge the sieve beds overboard in order to expose them to the lowpressure atmosphere. This method results in the purged gas notcontributing to pressurization, and being unavailable for use as anitrogen rich stream. Another aspect of the present invention includes ameans to create the required low pressure bed exposure without ductingthe purge gas overboard thereby also creating a nitrogen-rich byproduct.A highly simplified example of such a system's installation on anaircraft is illustrated in FIG. 4.

According to one aspect of the present invention, the producedhigh-oxygen concentration air is distributed in the air supply to theoccupant cabin(s). Based on appropriately positioned oxygenconcentration sensors, the system adjusts for maintaining the specifiedlevel(s) within the cabin(s). Still further, the byproduct ofnitrogen-rich gas is dispensed to those regions for which increasedflammability retardation is desirable. Schematically, this isdemonstrated in FIG. 4 where an air supply is introduced through anintake air duct 65 to a gas separator 70 where high concentration oxygenand nitrogen are produced. The oxygen enriched air flow or supply 80 isconveyed to the passenger cabin 50 while the nitrogen enriched air flowor supply 90 is directed to compartments 48 having heightenedflammability risks. Check valves 88 and 98 are provided to establishone-way conduction of the enriched flows 80 and 90.

An inter-compartment air mixer is shown as a fan 72. This feature isprovided to enable rapid remixing of the enriched gases in the eventthat conditions in the oxygenated passenger cabin are detected whichindicate that a reduced-flammability environment is desirable. Oneobvious example is the detection of combustion or smoke in theoxygenated cabin.

FIGS. 5 and 6 illustrate plan and elevational views, respectively, of anexemplary aircraft in which the presently disclosed invention(s) may beemployed. An aircraft interior 35 is defined within a fuselage 30 flyingin an ambient-air environment 25. On a macro level, a floor 37 definesseveral above-floor cabins including the cockpit 40, vestibule 54,occupant/passenger cabin 50, and lavatory/galley area 58. A baggagecompartment 43 is provided behind the occupiable cabins, but within thepressured zone, and which is often inaccessible from the cabin duringflight.

A non-pressured tail compartment 46 is shown behind a pressure barrier38 and houses primary components of the on-board gas processing plant. Agas separation unit 70 is depicted and to which an air supply 60,typically from one of the powering engines, is directed. Thisengine-warmed air (exemplarily 480 degrees F.) is expanded causing atemperature drop to, for example, 32 degrees F. at an intake duct 65.The pressure of this supplied air is then raised utilizing a series ofpressure blowers 68, between which heat exchangers are utilized toreduced the temperature-elevated pressured air flows.

The pressured air is then processed at the separator 70 wherehigh-concentration oxygen 80 and nitrogen 90 flows are generated. Thenitrogen is drawn off using suction pumps 91, between which heatexchangers 93 are utilized to keep the temperature of the nitrogenenriched air within manageable ranges.

The distributed flow rate of oxygen enriched air 80 iscomputer-controlled via a variable pass-through valve 84. The oxygenenriched air 80 may be directed forward in the aircraft 30 through duct82 or dumped overboard through port 87 depending upon the configurationof shuttle valve 86. The duct 82 is arranged below the floor 37 andpasses through both pressured and non-pressured zones across pressurebarrier walls 38. A check valve 88 assures unidirectional oxygen flow inthe duct 82. Switch valve 81 determines whether the oxygen enriched airsupply 80 is directed up past the floor and into the regular airdistribution ducts of the passenger cabin, or is diverted to anindividual, tube-based, direct passenger mask distribution system 89.

In the event that the oxygen enriched air is conveyed to the airdistribution ducts in the occupant cabins, piccolo tube(s) 83 areutilized having a series of apertures or distribution ports 85 ofcontinuously decreasing spacing. As depicted in FIG. 8, the spacedconfiguration of the apertures assures substantially even distributionof oxygen enriched air to the intended cabin areas.

The produced nitrogen enriched air flow 90 is similarly conveyed forwardin the craft via a check-valve 98 controlled distribution duct 92, andvariously dispensed to desirable locations. As can be best appreciatedin FIGS. 6 and 9, nitrogen enriched air is distributed to thebelow-floor compartment where it is essentially reservoired, as well asmore directly to such areas as the radio bays 49. Again, piccolo tube(s)94 are utilized having a series of apertures or distribution ports 95 ofcontinuously decreasing spacing. Still further, diversions of nitrogenenriched air can be effected by manipulation of control valve(s) 96 inorder to increase/decrease application of nitrogen enriched air, ondemand. For instance, if a combustion situation is detected in the aftradio bay 49 in the baggage compartment 43, a greater amount, or perhapsall of the produced nitrogen may be desirably dumped 97 at the radiorack 49.

Generally, the direction of air flow in the craft 30 is aft, forward. Inorder to divert odors out of the lavatory/galley area 58 and away fromthe passenger cabin, exhaust air ducting 59 is connected with theexhaust fan 72. The withdrawn air is dumped below the floor deck 37 intothe nitrogen enriched compartment. Advantageously, the exhaust fan 72can be strategically reversed in order to rapidly introduce nitrogenenriched air into the passenger cabin in the event that a lower oxygenconcentrate environment is desired. This feature may also be referred toas remixing.

It is contemplated that the control of the oxygen/nitrogen system may beautomated, at least in part, under the direction of a computer-basedcontroller 74. In at least one aspect, information can be obtainedutilizing above-floor 76 and below-floor 78 oxygen partial pressuresensors. Based on appropriate algorithmic processing of available data,the several control valves of the system can be variously manipulatedbased on deteimined requirements. Exemplary strategies of thecomputer-based controller 74 are depicted in the logic/function table ofFIG. 10.

With respect to such zeolite-based molecular sieve systems, certainimprovements in their performance and construction are alsocontemplated. As an example, because zeolites are temperature sensitive,one aspect of the present invention includes changing the temperature ofthe zeolite bed, preferably by heating, during the purge cycle toenhance release of the absorbed components, the same being primarilynitrogen. Similarly, in another embodiment, an electrical charge can beimposed on the zeolite bed, altering the molecular sieve-effects. Inthis context, it is appreciated that the magnitude of the charge may bemade variable so that the characteristics of a particular bed can bemanipulated.

1. A method for controlling a degree of oxygen/nitrogen shift ofincoming air in response to a partial pressure of oxygen in areas of anaircraft, said method comprising: dispensing an oxygen flow from ahigh-concentration oxygen supply to an occupant cabin of the aircraft inincrease the level of oxygen concentration within the occupant cabin;dispensing a nitrogen flow from a high-concentration nitrogen supply toa fire-susceptible, internal non-habitable region of the aircraft todecrease the capability for the atmosphere therein to supportcombustion; and varying the oxygen flow into the occupant cabin and thenitrogen flow into the occupant cabin based in part on a detectedcondition in the aircraft.
 2. The method of claim 1, wherein thedetected condition is at least one of a partial pressure of oxygenvalue, flight parameters, aircraft configuration, and smoke/fire warningstatus.
 3. The method of claim 1, further comprising: storing thehigh-concentration nitrogen supply in a first location prior todispensing the nitrogen from the high-concentration nitrogen supply. 4.The method of claim 3, wherein the first location is a reservoir.
 5. Themethod of claim 3, wherein the first location is a fire-susceptible,non-habitable area of the aircraft.
 6. The method of claim 1, furthercomprising: separating oxygen from ambient air onboard the aircraft toestablish a high-concentration oxygen supply; determining that anincreased oxygen concentration is desired in the occupant cabin; anddispensing oxygen from the high-concentration oxygen supply to theoccupant cabin of the aircraft thereby increasing a level of oxygenconcentration within the occupant cabin to a level greater than anaturally-occurring partial pressure of oxygen at an experiencedinternal occupant cabin pressure.
 7. The method of claim 6, furthercomprising: separating nitrogen from ambient air onboard the aircraft toestablish a high-concentration nitrogen supply; determining that reducedoxygen concentration is desired in the occupant cabin; and dispensinginto the occupant cabin nitrogen from the high-concentration nitrogensupply, thereby diluting the oxygen concentration in the occupant cabin.8. A method for controlling an atmosphere in habitable and non-habitableareas of an aircraft, said method comprising: establishing a supply ofnitrogen-rich air by separating nitrogen from air onboard the aircraft;storing the supply of nitrogen-rich air in a non-habitable area; andintroducing the nitrogen-rich air stored in the non-habitable area intoa habitable area, wherein the habitable area is habitable by passengersor crew.
 9. The method of claim 8, further comprising: establishing asupply of oxygen-rich air by separating oxygen from air onboard theaircraft; storing the supply of oxygen-rich air in a first location; andintroducing the oxygen-rich air stored in the first location into ahabitable area, wherein the habitable area is habitable by passengers orcrew.
 10. The method of claim 8, wherein the habitable area comprises atleast one of a passenger cabin, a cockpit, a lavatory, a galley, or avestibule.
 11. The method of claim 8, wherein the non-habitable areacomprises at least one of: a cabling duct, a baggage compartment, aradio rack compartment, or an electrical wiring compartment.
 12. Asystem for adjusting a nitrogen concentration and an oxygenconcentration within areas of an aircraft, the system comprising: a gasseparation unit to separate ambient air within an aircraft into anitrogen-rich flow and an oxygen-rich flow; a plurality of sensorsmonitoring at least one condition within at least one region of anaircraft; and a central control unit controlling a dispensation of thenitrogen-rich flow and the oxygen-rich flow based in part on an outputof the plurality of sensors.
 13. The system of claim 12, wherein thecentral control unit causes the dispensation of oxygen from theoxygen-rich flow into an occupant cabin if a higher oxygen concentrationin the occupant cabin is desired.
 14. The system of claim 12, whereinthe central control unit causes the dispensation of oxygen from theoxygen-rich flow to increase the oxygen concentration within an occupantcabin of the aircraft to a level greater than a naturally-occurringpartial pressure of oxygen at an experienced internal occupant cabinpressure.
 15. The system of claim 12, wherein the central control unitcauses the dispensation of nitrogen from the nitrogen-rich flow into anoccupant cabin if a reduced oxygen concentration in the occupant cabinis desired.
 16. The system of claim 12, wherein the central control unitcauses the dispensation of a portion of the oxygen-rich flow overboardif a reduced oxygen concentration in the occupant cabin is desired. 17.The system of claim 12, wherein the central control unit causes thedispensation of a portion of the nitrogen-rich flow overboard if areduced nitrogen concentration in the occupant cabin is desired.